In general, a method for coating a colored film on light-transmissive goods that directly receive a direct ray of light over a long period of time, such as glasses for vehicles or buildings, or a method for using glass, on a surface of which metal components are vacuum deposited, are used in order to block a portion of light. However, according to these methods, since a constant portion of visible rays are always blocked regardless of the light amount, there is a disadvantage in that a field of vision is hindered at night or cloudy weather.
In the related art, there were some products that are called a photochromic film. However, most of them are films that are obtained by masterbatching resins such as polyethylene, polypropylene, polystyrene, ABS and the like and extrusion molding them. Since these films mostly have the poor transparent property, they are used in fields that do not require a predetermined transparent property such as films for agriculture, and cannot be used as a photochromic film for vehicles that require an excellent field of vision.
In Korean Unexamined Patent Application Publication No. 2003-0089544, an effort in which a polyester (PET) film is used as a basic film, a photochromic acryl-based adhesive is coated on the film in an appropriate thickness to produce a photochromic film, and the photochromic film is used as a film for vehicle's suntan film is disclosed, but in this case, there is a problem in that since the durability property of the photochromic film is poor, the film is easily damaged.
Meanwhile, among methods for producing films including the photochromic film, a casting method, as shown in FIGS. 1 and 2, is carried out by inserting a soft or hard gasket between two cell casting plates made of glass and the like in order to control the thickness of the film, sealing it, filling it with a polymerizable raw material, curing it in a constant temperature water bath or oven, and separating the film.
There is no problem in production of the film that has the thickness more than 1 mm by using the above casting method, but when the thin film that has the thickness of not more than 1 mm is produced, there are problems in that the film is deformed, for example, wrinkles are formed on the film during the curing or defects are formed on the surface of the film. In particular, in comparison with the case of when a polymer as a material for forming a film is dissolved in a solvent and then used, in the case of when the monomer is directly injected into a mold and cast, since the film is shrunken while being polymerized and cured, it is very difficult to accomplish the uniformity of the thickness. However, in comparison with the case of when the polymer is used, in the case of when the film is molded by using the monomer, there is an advantage in that the density of film is increased. Accordingly, there is a need to develop a technology for producing a film that has a thickness of not more than 1 mm by using monomers without the above problems.